1. Field of the Invention
This invention relates to the art of electrostatic recording and more particularly, to an electrostatic recording head of the type which comprises ion-generating units each including a dielectric electrode, a discharge electrode, an insulating layer sandwiched between the electrodes, and an ion flow control unit formed of a screen electrode.
2. Description of the Related Art
As an electrostatic recording head is known in which ions are generated or produced and images are recorded by use of the generated ions (U.S. Pat. No. 4,408,214).
FIGS. 6, 7 and 8 are, respectively, illustrative views of a known electrostatic recording head wherein FIG. 6 is a schematic sectional view of an essential part of the head, FIG. 7 is an illustrative sectional view of the head, taken along the line VII--VII of FIG. 6, and FIG. 8 is a schematic sectional view of the head, taken along the line VIII--VIII of FIG. 7.
As is particularly shown in FIGS. 6, 7 and 8, an electrostatic recording head Ho includes an insulating substrate 01, and dielectric electrode strips 02, a first insulating layer 03, discharge electrode strips 04, and a second insulating layer 05 formed on the substrate 01 in this order in such a way that the discharge electrode strips 04 are each arranged as being crossed with individual dielectric electrode strips 02 as shown in FIG. 7. The second insulating layer 05 has a space region 06, wherein ions are generated, at individual crossed portions of each discharge electrode strip 04 and each dielectric electrode strip 02.
A screen electrode 07 is further formed on the second insulating layer 05 of the insulating substrate 01. The screen electrode 07 has an opening 08 for ion passage corresponding to each space region 06. Thus, the crossed portions, space regions 06, and openings 08 are arranged in a matrix in the plan view of FIG. 7.
An ion generating unit includes an AC power supply 010, from which a high frequency high voltage is applied between the dielectric electrode strips 02 and the discharge electrode strips 04, and the elements or members indicated by the reference numerals 2 to 6. This application of voltages causes ions to be generated in individual space regions 06 as desired.
An ion flow control power supply 011 is connected to the respective dielectric electrode strips. From the power supply 011, an ion flow control potential is outputted thereby generating an electric field for the ion flow control between the discharge electrode strips 04 and the screen electrode 07. The ion flow control unit includes the ion flow control power supply 011 and the elements or members indicated by the reference numerals 04 to 07.
The respective electrodes 02, 04 and 07 are connected with a DC bias power supply 012 capable of generating a bias potential against an electrostatic latent image-bearing material (dielectric drum) not shown.
The electrostatic recording head having the arrangement as set out above operates as follows: the ions generated in intended space regions 06 by means of a high frequency high voltage transmission from the AC power supply 010 are accelerated or absorbed by application of an electric field established between the discharge electrode strips 04 and the screen electrode 07 to discharge a controlled ion flow is discharged thereby forming an electrostatic latent image according to image signals.
In the prior art electrostatic recording heads, the material for the screen electrode is usually nickel, stainless steels and the like (Japanese Laid-open Patent Application Nos. 54-78134, 63-53056 and 2-4541).
In this type of recording head, however, the electrodes are most likely to suffer corrosion by means of various active species generated during the course of the discharge. Especially, with the screen electrode, the considerable corrosion takes place at the side faces, which establish part of the ion generating space regions 06 and are thus invariably exposed to the active species, corrosion also takes place at the inner sides of the openings 08. In the worst case, the openings 08 may be clogged, resulting in a substantial lowering of ion output. These previously employed electrode materials are not satisfactory with respect to corrosion resistance.